appetite Flashcards
a)What 3 factors affect thirst control and b)which of these has the biggest impact?
a)Plasma osmolality, blood volume, blood pressure
b)plasma osmolality (2-3% change has same effect as 10-15% change in blood volume/ arterial pressure)
action of vasopressin
Acts on the kidneys to regulate the volume & osmolality of urine
Collecting duct - Aquaporin 2 channel
When plasma ADH is low a large volume of urine is excreted (water diuresis)
When plasma ADH is high a small volume of urine is excreted (anti diuresis).
Where are osmoreceptors found?
Hypothalamus- organum vasculosum lamina terminalis (OVLT) and subfornical organ
How do osmoreceptors stimulate ADH release?
Increase in plasma osmolarity–> water leaves osmoreceptors by osmosis–> osmoreceptor shrinks–> increased proportion of cation channels and membrane depolarisation–> signal ADH producing cells to produce more ADH–>fluid retention
How is thirst sensation reduced before sufficient water has been absorbed by GI tract to correct plasma osmolarity?
Through sensory receptors in the mouth, pharynx and oesophagus
This relief of thirst sensation is short lived
Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected.
Describe how angiotensin II is produced in RAAS?
Low blood pressure detected by juxtaglomerular cells in renal afferent arteriole–> kidney produces renin–> acts on angiotensinogen from liver and produces angiotensin I–> this travels to lungs and forms angiotensin II through action of ACE
Functions of angiotensin II?
Stimulates aldosterone production through action on zone glomerulosa of adrenal glands (consequent water retention through increased NaCl reabsorption/K+ excretion)
Stimulates ADH secretion
Vasoconstriction and increased sympathetic activity
Thirst
What factors act on hypothalamus for appetite regulation?
-Ghrelin, PYY and other gut hormones
-Leptin
-Neural input from periphery/ other brain regions
What does orexigenic mean?
Appetite stimulant
What does anorectic mean?
Appetite suppressant
What regions of the hypothalamus contribute to appetite regulation?
Arcuate nucleus, paraventricular nucleus, lateral hypothalamus, ventromedial hypothalamus
How does the arcuate nucleus regulate appetite?
Integration of peripheral and central feeding signals- it has an incomplete BBB which can allow access to peripheral hormones
What are the two neuronal populations in the arcuate nucleus?
NPY/AGrP neurons (Stimulatory- increase feeding through action on paraventricular nucleus)
POMC neurons (inhibitory- decrease feeding through action on paraventricular nucleus)
Describe the melanocortin system
What CNS mutations can cause obesity?
Decreased POMC/ MC4R
(No NPY or AgRP mutations associated with appetite in humans.)
